Ethylene and propylene, which are important raw materials of petrochemical products, are prepared by cracking hydrocarbon, which uses paraffin compound such as natural gas, naphtha, gas oil, etc., as main components, at a high temperature of at least 800° C. in the presence of a steam.
In the hydrocarbon steam cracking reaction, in order to increase the yield of ethylene and propylene, the conversion ratio of hydrocarbon should be increased or the selectivity of olefin should be increased. However, since there is a limitation in increasing the conversion ratio of hydrocarbon or the selectivity of olefin only by the pure steam cracking reaction, various methods capable of increasing the yield of olefin have been proposed.
In the hydrocarbon steam cracking reaction, there has been proposed the steam cracking method using a catalyst as the method capable of improving the yield of ethylene and propylene. U.S. Pat. No. 3,644,557 disclosed a method of using a catalyst made of magnesium oxide and zirconium oxide, U.S. Pat. No. 3,969,542 disclosed a method of using a catalyst including calcium aluminate as basic components, U.S. Pat. No. 4,111,793 disclosed manganese oxide carried in zirconium oxide, EP Laid-Open Patent No. 0212320 disclosed an iron catalyst carried in magnesium oxide, and U.S. Pat. No. 5,600,051 disclosed a catalyst made of barium oxide, alumina, and silica. In addition, PCT Patent No. 2004/105939 disclosed a method of using a catalyst made of potassium magnesium phosphate, silica, and alumina. However, in the case of using these catalysts, the catalyst material functions as a thermal medium in the carbon steam cracking reaction to improve the yield of olefin, however, is slight in the yield improvement of olefin as compared to the case of using a non-active carrier.
Russia Patent No. 1,011,236 disclosed a potassium vanadate catalyst formulated with boron oxide in an alumina carrier. However, in the case of using alkali metal oxide or potassium vanadate catalyst, the yield improvement of olefin by the catalyst becomes small as well as the loss of olefin essentially occurs at high temperature for hydrocarbon decomposition. In other words, the catalyst can exist in a liquid phase in the inside of a high-temperature cracking reactor due to a low melting point of catalyst components and the catalyst components are volatilized due to the fast flow of reaction gas to degrade the catalyst activation as the reaction time elapses.
U.S. Pat. No. 7,026,263 disclosed a method of using a hybrid catalyst made of molybdenum oxide, alumina, silica, silicalite, zirconium oxide, etc. Since the above-mentioned catalysts can react at low reaction temperature, but is operated at very low hydrocarbon flux, it is difficult to directly apply the catalysts to the existing processes. In addition, the thermal stability of catalysts is significantly low at the reaction temperature of at least 700 to 800° C., such that the catalyst activation is lost.
In addition, since the existing cracking process is operated at high reaction temperature and high hydrocarbon linear velocity and generates a large amount of coke, the generated coke should be combusted at high temperature. In order to use the catalyst for a long time under the severe operation conditions, the catalysts should be stabilized against the thermal/physical deformations. The foregoing related arts have a problem in that the catalysts are vulnerable to the thermal/physical deformations or the stability thereof is not verified.
Therefore, in order to consider economical efficiency of hydrocarbon steam cracking process and to avoid the complexity of processes, a need exists for a catalyst that significantly improves the yield and selectivity of light olefins and has excellent thermal/mechanical stability even at high temperature.